Form 5330 – IRS Excise Tax Filing Guide for 4975, 4979, 4980

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A controller calls because a 401(k) deferral hit the trust a few business days after payroll instead of the same day, and wants to know whether it really matters. It does. Once participant money can be reasonably segregated from employer assets it becomes a plan asset, and a late deposit becomes a prohibited transaction under section 4975. Small plans get a seven business day safe harbor, but past that, the clock starts running on an excise tax.

Form 5330 is where you report and pay that tax, along with the others tied to benefit plans under sections 4979 and 4980. The initial prohibited-transaction tax is generally 15 percent of the amount involved and climbs to 100 percent if you do not correct it in time, and the due dates split by code section: most of these land the last day of the 7th month after the employer's tax year, while a 4979 excess contribution follows a 15-month deadline from plan year end.

Key Takeaways

• IRS Form 5330 is how you report and pay excise taxes tied to retirement plan issues, including prohibited transactions under section 4975, excess contribution refunds under section 4979, and plan asset reversions under section 4980.
• Due dates differ by code section. For most 4975 filings, the due date is the last day of the seventh month after the filer’s tax year end. For 4979, it is the last day of the fifteenth month after the plan year end. For 4980 reversions, it is the last day of the month following the month of the reversion.
• Request a Form 5330 filing extension on Form 5558. An extension to file does not extend time to pay.
• For prohibited transactions, the initial excise tax is generally 15 percent of the “amount involved,” rising to 100 percent if not corrected within the taxable period.
• Late deposits are prohibited transactions because participant contributions become plan assets as soon as they can be reasonably segregated from employer assets. Small plans have a seven business day safe harbor.

What Form 5330 Is, In Plain English

Form 5330 is the IRS return for reporting excise taxes when a qualified plan or its stakeholders trip certain compliance wires. In day‑to‑day practice you will see it most for three situations:

• Late deposits of employee deferrals or loan repayments, which the IRS treats as prohibited transactions under section 4975.
• ADP or ACP refund timing failures under section 4979.
• Defined benefit or other qualified plan asset reversions taxed under section 4980.

Who files? The person responsible varies by provision. For section 4975 prohibited transactions, any disqualified person who participated, often the employer or another party in interest, files and pays. For section 4980 reversions, the employer pays. Per the form's instructions, you can only complete one section of Part I for each Form 5330 filed, so if multiple excise taxes apply you file a separate Form 5330 for each section (and additional separate returns are required when due dates differ or for separate plans).

Deadlines are not one size fits all:

• Section 4975, including late deposits, is generally due the last day of the seventh month after the filer’s tax year end.
• Section 4979 is due the last day of the fifteenth month after the plan year end.
• Section 4980 reversions are due the last day of the month after the month of the reversion. Build your calendar around those anchor rules.

Extension requests run through Form 5558. Tax must be paid by the original due date, and penalties for late filing or late payment can stack quickly.

Why Firms End Up Here

You are not short on clients. You are short on repeatable delivery when compliance gets messy. The usual culprits:

• Payroll cut on Friday, cash posted on Wednesday, contributions sat in the operating account too long.
• ADP/ACP refunds queued, then fiscal close hit, and the fifteenth‑month deadline slipped.
• A DB plan termination with residual assets moved faster than the documentation, and now a reversion tax clock is ticking.

When production spikes, review loops stall and documentation thins out. That is exactly when Form 5330 risk shows up. The fix starts with understanding when money becomes a plan asset and how the IRS wants you to compute the “amount involved.” We will take those one at a time.

When Employee Money Becomes a Plan Asset

For ERISA and Code section 4975, participant contributions and loan repayments become plan assets as soon as you can reasonably segregate them from the employer’s general assets. For plans with fewer than 100 participants, a seven business day deposit safe harbor applies. The old “15th business day of the following month” is not a safe harbor, it is a maximum outer limit in the regulation. If you can segregate sooner, you must deposit sooner.

That timing matters. If deposits are late, you have a prohibited transaction. The disqualified person who participated generally owes the section 4975 excise tax and must file Form 5330, Schedule C.

Practical tip: document your normal payroll‑to‑trust timeline and keep short notes when unusual events, like a bank outage, push you off the pattern. It is your best evidence of what “reasonably segregated” means for your operation.

How the IRS Wants You To Calculate the “Amount Involved”

You do not guess the tax. For a late deposit prohibited transaction, the IRS uses a use‑of‑money method. In simple terms, you calculate interest on the withheld contributions from the date the money should have been in the plan until the date you corrected, using the IRS underpayment rate in section 6621. That interest figure is the “amount involved,” and the excise tax is generally 15 percent of that amount for each tax year in the taxable period.

Step‑by‑Step, Using Rev. Rul. 2006‑38

• Identify the deposit that was late and the date it should have hit the plan trust.
• Apply the quarterly IRS underpayment rate under section 6621 for the period of the delay.
• Compute interest on the principal for each affected period until correction.
• If the delay crosses into a new tax year before correction, treat it as a new prohibited transaction for that year and compute again, then total the first‑tier 15 percent excise tax for each year.

The IRS’s example in Rev. Rul. 2006‑38 shows a late deposit across two tax years. The “amount involved” is the interest on the withheld contributions, and the 15 percent first‑tier excise tax is applied separately to each year’s amount.

A Quick Numeric Example

• Pay date: December 8. Contribution deposited: December 30 of the next year.
• Principal at risk: 100,000. Underpayment rate at 5 percent each year, as a simple illustration.
• Interest for first period, December 8 through December 31 of Year 1, then for Year 2 until December 30, compounded as the ruling describes.
• Excise tax equals 15 percent of the Year 1 amount, plus 15 percent of the Year 2 amount. If you do not correct and the taxable period continues, the IRS can impose an additional tax up to 100 percent.

When a Late Deposit Becomes a Prohibited Transaction

Participant contributions and loan repayments become plan assets as soon as you can reasonably segregate them from your general assets. For small plans, there is a seven business day safe harbor. If you can segregate sooner, you must deposit sooner. A deposit later than that is a prohibited transaction, and the responsible disqualified person generally files Form 5330 and pays the excise tax.

Document your normal payroll‑to‑trust timetable, then keep short notes when unusual outages or holidays alter timing. Your pattern is your best evidence of what “reasonably segregated” means in your shop.

About that “14‑Day” Idea

You may have heard you can fix certain prohibited transactions within 14 days and avoid the tax. That statutory correction period exists, but it applies to specific securities or commodities transactions described in 4975(d)(23), not to most late deposit cases. Do not rely on a generic 14‑day window for late 401(k) deposits.

Filing Deadlines, Extensions, and Penalties

Deadlines vary by Code section, and they do not line up with Form 5500. Anchor on these rules as of December 30, 2025:

• Section 4975, including late deposits and other prohibited transactions, is due the last day of the seventh month after the filer’s tax year end.
• Section 4979 for ADP/ACP excesses is due the last day of the fifteenth month after the plan year end (Section 4979 is unique in this respect; most other plan‑year‑based Form 5330 taxes use a 10‑month deadline, so do not default to the shorter window).
• Section 4980 reversions are due the last day of the month after the month of the reversion.

You can request a filing extension using Form 5558. This extends time to file, not time to pay, so you still pay any estimated excise tax by the original due date to avoid late‑payment penalties and interest.

Late filing can trigger a penalty of 5 percent per month, up to 25 percent of the unpaid tax, plus a separate late‑payment penalty and interest. Reasonable‑cause relief is possible, but you must document it.

Mandatory e‑Filing Threshold

If you file at least 10 returns of any type during the calendar year the Form 5330 is due, you must e‑file Form 5330. Others are encouraged to e‑file, though paper filing to the Ogden Service Center remains available.

ADP/ACP Excise Tax Basics Under Section 4979

Section 4979 applies when ADP or ACP corrections are not distributed or forfeited by the statutory deadline. The default correction window is 2½ months after the plan year end, extended to 6 months for EACA plans. If you miss those windows, the excise tax applies and is reported on Form 5330, due the last day of the fifteenth month after the plan year end.

Practical ways to avoid 4979 tax

• Lock a standing calendar for March 15 corrections on calendar‑year plans, and use a separate EACA calendar for June 30.
• Pre‑run ADP/ACP testing two to three payrolls before plan year end to flag likely refunds.
• Tighten payroll feeds so refunds can be processed within days, not weeks.

Plan Asset Reversions, Section 4980

When assets revert to the employer, section 4980 imposes an excise tax. The default rate is 50 percent. The reduced 20 percent rate applies only if you establish a qualified replacement plan or provide certain pro‑rata benefit increases, and the filer must justify the reduced rate on Schedule I line 4 (Schedule I actually treats 50 percent as the default rate and requires the filer to explain on line 4 why they qualify for the reduced 20 percent rate, so document the justification before filing). File Form 5330 by the last day of the month after the month of reversion.

A short checklist before any reversion

• Confirm plan document authority for distribution of residual assets and required notices.
• Model the excise tax rate with and without a qualified replacement plan.
• Calendar the reversion date and prepare the Form 5330 schedule and payment.

Who Must File Form 5330

For section 4975 prohibited transactions, any disqualified person who participated in the transaction generally must file Form 5330. This often includes the employer, certain fiduciaries, or service providers. For section 4980 reversions, the employer files. For section 4979 ADP/ACP issues, the employer files. The form’s instructions outline who files by section and make clear that multi‑year transactions can require multiple annual filings until corrected.

Quick reference table

Who files	Trigger	Notes
Employer or other disqualified person	Late deferrals or loan repayments, or other prohibited transactions under 4975	Compute “amount involved” using Rev. Rul. 2006‑38 for late deposits, then apply 15 percent per affected year.
Employer	ADP/ACP excise under 4979	Due last day of the fifteenth month after plan year end.
Employer	Plan asset reversion under 4980	50 percent default rate, reduced to 20 percent only if a qualified replacement plan is established or required pro‑rata benefit increases are provided (justified on Schedule I line 4).

Coordinating IRS and DOL Rules Without Tripping Over Yourself

The IRS and the DOL measure late deposits differently. The IRS “amount involved” is use‑of‑money interest that drives the 4975 excise tax. The DOL focuses on restoring lost earnings to participants. These will not be the same number. Reconcile the two sets of calculations in your memo so your reviewer and auditor can tie out why the amounts differ.

Think of it this way, the DOL asks, did participants get made whole, including earnings, and did you document it, while the IRS asks, what was the employer’s economic use of plan assets, priced at the section 6621 rate.

Correction Pathways That Can Limit or Eliminate Excise Tax

You have two practical tracks, depending on the size and timing of the error.

• VFCP Self‑Correction Component, for smaller late deposits and loan repayment delays with lost earnings totaling 1,000 or less, corrected within 180 days. You compute and restore lost earnings using the DOL calculator, notify EBSA through its web tool, retain records, and receive an acknowledgment email rather than a no‑action letter.
• Full VFCP filing with EBSA for larger or more complex cases, which can pair with PTE 2002‑51 excise tax relief if you satisfy conditions, including documentation and, where applicable, paying the otherwise‑due excise amount to the plan. Recent amendments expanded relief and removed the once‑every‑three‑years limitation. Effective March 17, 2025.

The SCC can be fast, but it has guardrails. Miss the 180‑day window or exceed the 1,000 lost‑earnings cap and you are back to a full VFCP application or traditional correction plus Form 5330.

How SCC and PTE 2002‑51 work together

Under the 2025 amendments, if you properly self‑correct a qualifying late deposit under the SCC, you can rely on PTE 2002‑51 to waive the IRS excise tax provided you deposit an amount equal to that excise into the plan as additional earnings and keep a completed Form 5330 calculation in your files. That documentation is mandatory even though you do not submit the form to EBSA.

Avoiding Pyramiding And Multi‑Year Exposure

A continuing prohibited transaction, like a late deposit that crosses tax years, can create a new transaction on the first day of each succeeding tax year until you correct it. That is how exposure pyramids. Stop the clock by correcting quickly, then file Form 5330 for each affected tax year by its seventh‑month deadline. Keep a tight memo that shows the plan‑asset dates, deposit dates, 6621 rates used, and your reconciliation to DOL lost earnings.

A simple three‑step containment plan

• Identify the earliest date the funds could have been segregated, then compute IRS and DOL numbers side by side.
• Correct contributions and lost earnings first, then decide whether SCC, full VFCP, or straight Form 5330 is the right path.
• Calendar the filing due dates by section and get any needed Form 5558 in before the original deadline.

Filing Logistics, From IDs To Attachments

• E‑file through an IRS Authorized e‑file Provider when practical. If you file 10 or more returns of any type for the year, you must e‑file Form 5330. Paper filers mail to the Ogden Service Center.
• File separate Forms 5330 when sections have different due dates or when different plans are involved. One Form 5558 per section per plan for differing due dates.
• Sign the return, include the PTIN if a practitioner prepares it, and keep your calculation workpapers with section 6621 rates and deposit dates.

Attachments most reviewers expect to see

• A short narrative describing the failure, discovery date, and correction steps.
• Your “amount involved” schedule with 6621 interest rates and daily factors as needed.
• A reconciliation to DOL lost earnings and, if using SCC or VFCP, a copy of the EBSA acknowledgment or submission receipt.

Small, Repeatable Controls That Prevent Repeat Issues

• Standardize payroll‑to‑trust timing with a written SOP and back‑up deposit method for holiday weeks.
• Automate a bank rule that flags any contribution file not posted by Day 2, so someone reviews on Day 3.
• Keep an “incident log” that captures delays, causes, and fixes to support reasonableness under the plan‑asset rule.

If your team juggles audits, tax deadlines, and onboarding, outsource repetition, not judgment. The work that always slips is the work without a named owner and a visible clock.

Where Accountably Fits

If you are tired of scrambling each season, Accountably can embed trained offshore teams into your delivery system so the SOPs, workpapers, review checkpoints, and filing calendars actually run every week. We work inside your systems, document “amount involved” under Rev. Rul. 2006‑38, prepare Form 5330 e‑file packages, and keep your VFCP evidence tight. You keep control, we add capacity and structure. Use this only if you want fewer surprises and faster reviews.

Quick Reference, Dates And Sections

Section	What triggers it	Form 5330 due date	First‑tier tax
4975	Prohibited transactions, including late deferrals or loan repayments	Last day of the 7th month after filer’s tax year end	15% of amount involved per year, up to an additional 100% if not corrected
4979	ADP/ACP corrections not made by 2½ months after plan year end, or 6 months for EACA	Last day of the 15th month after plan year end	10% of excess amounts, see instructions for specifics
4980	Employer reversion of plan assets	Last day of the month after month of reversion	50% default, reduced to 20% only with a qualified replacement plan or required pro-rata benefit increases (justified on Schedule I line 4)

Notes that save headaches

• Separate returns when sections have different due dates, even if it is the same plan.
• The ADP/ACP distribution timing drives whether 4979 applies, not the date you complete the Form 5330.
• For reversions, model the 20 percent vs 50 percent outcome before the board votes.

Worked Example, Start To Finish

Imagine your calendar‑year C‑corp missed one 401(k) deposit from December 8, 2024, and corrected on January 10, 2025.

• Plan asset rule triggers a prohibited transaction as of the earliest date you could reasonably segregate the funds. Assume that was December 9, 2024.
• Apply the 6621 underpayment rate in effect on December 9, 2024 to compute interest through December 31, 2024, then apply the appropriate 2025 rate for January 1 through January 10, 2025, compounding as described in the ruling. That interest is your “amount involved” for each year.
• File Form 5330 for the 2024 tax year by July 31, 2025, and for 2025 by July 31, 2026, unless you obtain Form 5558 extensions. Pay the 15 percent first‑tier excise for each year. If you used SCC and qualify for PTE 2002‑51 relief, deposit the excise amount into the plan instead and retain your finished Form 5330 calculation in your files.

A Short SOP You Can Copy

• Within one business day after payroll, reconcile the 401(k) funding file.
• By business day two, initiate the ACH or wire.
• If funds are not in the trust by business day three, escalate to an operations lead.
• If any deposit misses your standard window, start a one‑page incident log, compute DOL lost earnings, and determine if SCC applies.
• Reconcile DOL lost earnings to IRS “amount involved,” then decide on VFCP or Form 5330 filing.

Your Action Plan For This Week

• Audit last year’s payroll‑to‑trust dates and flag any outliers.
• Map which section you might trigger, then pencil in your real due dates for 4975, 4979, or 4980.
• Build a one‑page calculator for the IRS “amount involved” using the 6621 rate and a separate DOL lost earnings tab.
• Decide whether SCC, full VFCP, or straight Form 5330 is the cleanest path for each item.

Precision now beats explanations later. The sooner you quantify the issue and choose a path, the lower the total cost.

Final Word

You do not need more stress, you need a clear recipe. Form 5330 becomes manageable when you know which section you are in, how to compute the “amount involved,” and the real deadline on your calendar. If you want help building the SOPs, workpapers, and review checkpoints so this runs in the background all year, our team at Accountably can plug into your systems and keep the wheels turning while you focus on clients and advisory work.

Common Mistakes We See Every Season

These five errors create the most rework when we step into a Form 5330 file. Each one starts as a small misread of the instructions, then multiplies across schedules, deadlines, or per-day penalty math.

Reusable Checklists

These three checklists are copy-paste ready for your firm's plan-administration SOPs. Each one covers a discrete Form 5330 workflow we run every season, with steps tight enough to drop into a tax-prep packet without modification.

Keep 5330 Season From Stalling

Form 5330 traffic does not run on a single seasonal cycle. Per the IRS Form 5330 instructions (revised December 2025), the form covers excise taxes under twelve different IRC sections, and each section has its own deadline tied to either the employer's tax year, the plan year, or the date of a specific event. A single client may need three separate Form 5330 returns in one calendar year if a late 401(k) deposit, an ADP/ACP failure, and a plan reversion all hit the same plan.

The fix is not faster filing, it is a tracking discipline. Once you treat Form 5330 like a side-system of recurring micro-deadlines instead of a once-a-year return, the workpapers, schedules, and review cycles fall into place.

• Maintain a Form 5330 tracker per plan that maps each section to the right deadline anchor: employer tax year for Section A (4975, 4972, 4978), plan year for Section B (4971) and Section C (4979), calendar year for Section B1 (4977), reversion month for Section D (4980), and entity-manager tax year for Section F (4965).
• File a separate Form 5330 for each Part I section, since the form only allows one section per return.
• Use Form 5558 to extend the filing date and to pre-pay the tax, with the payment picked up on Form 5330 Part II line 18.
• Flag Section C (4979 excess contributions, Schedule H) separately, since the 15-month deadline runs longer than the 10-month deadline most plan-year-based Form 5330 taxes follow.
• Default the Section 4980 reversion rate to 50% in the workpaper template, and only switch to 20% with a documented Schedule I line 4 justification.

Accountably's tax compliance team builds this Form 5330 tracking layer into a firm's existing plan-administration workflow, so excise tax exposure surfaces during the annual plan review instead of three months after the deadline.

FAQs

What is IRS Form 5330 used for?

Form 5330 reports and pays excise taxes related to employee benefit plans, including prohibited transactions under section 4975, ADP/ACP excise taxes under section 4979, reversions under section 4980, and other listed sections. You file it for each year a prohibited transaction remains uncorrected, and you file separate returns when due dates differ.

What is the penalty for filing Form 5330 late?

The late filing penalty is generally 5 percent per month of unpaid tax, up to 25 percent, plus a separate late payment penalty and interest. Reasonable‑cause relief may be available, but interest still accrues until paid.

Who prepares Form 5330?

You can prepare it in‑house or use your TPA or ERISA counsel for complex cases. Ensure the signer has authority, include the PTIN if a practitioner prepares it, and keep the schedules that support your “amount involved” and any VFCP or SCC documentation.

Is there really a 14‑day window to avoid the 4975 excise tax?

There is a 14‑day correction period in the Code, but it applies to specific securities or commodities transactions and does not generally eliminate excise liability for late 401(k) deposits. For late deposits, look to SCC, full VFCP, or file Form 5330.

Do I need to e‑file Form 5330?

If you file at least 10 returns of any type in the year the 5330 is due, you must e‑file Form 5330. Others are encouraged to e‑file. Paper filers mail to Ogden.